Torque limiter having automatic reset function

ABSTRACT

A torque limiter adapted to be automatically reset after a long period of time. The inner ring (1) has a cylindrical surface (5). A polygonal engaging surface (9) is formed on the outer ring (2) by a leaf spring in the shape of a polygonal ring. A cage (11) having pockets is provided between the inner and outer rings (1, 2). Rollers (13) received in the pockets are adapted to engage the cylindrical surface (5) and the engaging surface (9) at the narrowest portions. The inner ring (1) has an eccentric surface (15) on which is supported a bearing (16) which holds the cage (11) in a diametrically offset position. An annular portion (20) of the cage (11) is brought into contact with an annular portion (19) of the outer ring (2). As the torque increases with the rollers (13) engaged, the leaf spring (8) is deformed and the rollers (13) pass through the engaging positions, so that the clutch is disengaged. The cage (11) is further rotated by the torque transmitted from the inner ring, kept in contact with the annular portion (19) of the outer ring. Creeping thus occurs and the cage and thus the rollers are moved slowly to the next engaging positions.

TECHNICAL BACKGROUND

This invention relates to a torque limiter having an automatic resetfunction.

BACKGROUND ART

In ordinary industrial machines, various means are used to transmitpower by rotation, such as belts, pulleys, gears and shaft coupling. Inorder to increase the reliability of the entire machine and to preventany fatal accident, an increasingly greater number of machines areprovided with safety devices for preventing excessive loads on criticalparts thereof.

It is especially important to provide a propeller engine of a small shipor a compression circuit in a compressor for a refrigerator with asafety device for cutting off torque transmission from the engine if thedriven side is subjected to an excessive load.

A shear pin shown in FIG. 20 is one of such safety devices. This shearpin 71 is inserted between a driving shaft 72 and a driven member 75(propeller in the illustrated example). If the driven member issubjected to an excessive load, the pin 71 is broken, allowing thedriving shaft 72 to run idle.

But such a shear pin has to be replaced with a new one every time thedriven member is repaired. Such a replacement is troublesome. If such ashear pin is used for a propeller shaft of a small ship, pins have to bereplaced while on the sea. Such a job thus involves a lot of trouble anddanger.

A safety device of the type having an automatic reset function and thususable repeatedly is known as a torque limiter, as shown in FIG. 21.This torque limiter has balls 82 held in position by a hub 81 coupled toa driven member and received in pockets 85 formed in a driving flange84. Springs 83 are provided to bias the balls 82 against the pockets 85.If the hub 81 is subjected to an excessive load, the balls 82 get out ofthe pockets 85, thus cutting off torque transmission. As the drivingflange 84 further rotates, each ball 82 will get into another pocket 85.The torque limiter is thus automatically reset and the hub 81 resumesits function.

With this type of torque limiter, automatic resetting occurs too soonbefore the driving side member and the driven side member make onerotation relative to each other. Thus, even if the torque limiter shouldstop due to some malfunction of the driven side, it will beautomatically reset repeatedly at very short time intervals as far asthe driving side is rotating at a high speed. For example, if thedriving flange 84 is rotating at 1800 rpm, the balls 82 will repeatedlycome into and out of the pockets at the rate of 350 times or more persecond to restart torque transmission. This will not only wear thecontact parts markedly but the device at the driven side will also besubjected to undue forces because it is restarted soon after it hasfailed.

It is therefore an object of this invention to provide a torque limiterwhich is adapted to reset not immediately but after a predetermined longperiod of time after clutch has disengaged due to some malfunction atthe driven side.

DISCLOSURE OF THE INVENTION

In order to solve the above problems, there is provided, as a firstmeans of this invention, a torque limiter having an automatic resetfunction comprising two bearing rings fitted one on the other, one ofthe bearing rings being connected to a driving side and the other to adriven side, the bearing rings having surfaces opposed to each other,one of the opposed surfaces being a cylindrical surface, the other ofthe opposed surfaces being engaging surfaces, a cage formed with aplurality of pockets and mounted between the bearing rings, engagingelements each received in the pockets and adapted to engage thecylindrical surface and the engaging surfaces, one of the cylindricalsurface and the engaging surfaces having their portions to be broughtinto contact with the engaging elements made elastically deformable, anda decelerating means coupled to the cage for transmitting the rotationof the bearing ring connected to the driving side to the cage afterdecelerating it.

In the second means of this invention, the engaging surfaces form apolygonal surface.

In the third means of this invention, the decelerating means comprisestwo annular portions fitted one on the other with a gap definedtherebetween and adapted to rotate together with the bearing ringconnected to the driven side and the cage, respectively, and aneccentricity imparting means for offsetting one of the annular portionsto bring it into contact with the other annular portion.

In the fourth means of this invention, the decelerating means comprisestwo annular portions fitted one on the other with a gap definedtherebetween and adapted to rotate together with the bearing ringconnected to the driven side and the cage, respectively, and rollingelements press-fitted between the cage and the bearing ring connected tothe driving side fop bringing the annular portions into contact witheach other by deforming the annular portion adapted to rotate togetherwith the cage.

In the fifth means of this invention, the cylindrical surface and theengaging surfaces have their engaging portions formed of plate-shapedresilient members, and recesses are formed behind the resilient membersto permit deformation of the resilient members.

In the sixth means of this invention, the resilient member is providedwith a protrusion extending toward the engaging surface or thecylindrical surface.

In the seventh means of this invention, the bearing ring connected tothe driven side is integrally provided with a power transmission meanssuch as a gear, a belt groove or a spline.

In the first means, as the bearing rings rotate relative to each other,the engaging elements engage the cylindrical surface and the engagingsurface. The clutch is engaged, allowing both rings to rotate together.

In this state, if the bearing ring connected to the driven side issubjected to an excessive load, the cylindrical surface or the engagingsurfaces will be elastically deformed, allowing the engaging elements topass the engaging positions. The clutch thus disengages.

After the engaging elements have passed the engaging positions, they aremoved to the next engaging positions by the cage. But since the cage isdecelerated by the decelerating means so as to rotate at a slower speedthan the bearing ring connected to the driving side, the engagingelements move at a correspondingly slow speed. Thus, it takes a longtime until each engaging element reaches the next engaging position.When the engaging elements reach their next engaging positions, theclutch engages again.

In the second means, the engaging surfaces form a polygonal shape. Inother words, many engaging surfaces are arranged circumferentially.Thus, many engaging elements can be mounted between the cylindricalsurface and the engaging surfaces. This increases the torquetransmittable by the torque limiter.

In the third and fourth means, when moving the engaging elements fromone engaging position to the next, the cage is driven in the directionof rotation while kept in contact with the annular portions fittedtogether. As the annular portions rotate while kept in contact with eachother, creeping occurs, so that the annular portions move in acircumferential direction relative to each other by a distance equal tothe engaging gap δ multiplied by π. Thus, by setting the engaging gap δat a sufficiently small value with respect to the nominal diameter ofthe annular portions, the time required for the engaging elements toreach the next engaging positions can be prolonged to a considerabledegree.

In the above means, the annular portions may be provided integral withthe bearing ring at the driven side and the cage, respectively, or maybe provided on members which rotate together with the bearing ring atthe driven side and the cage.

In the fifth and sixth means, as the engaging elements approach thenarrowest portions between the cylindrical surface and the engagingsurfaces, the resilient members are deformed toward the recesses formedbehind them. They are deformed markedly because the engaging elementsengage the protrusions provided on the resilient members. A largebending stress is thus produced in the resilient members and a largeresilient repulsion force is applied from the resilient members to theengaging elements. A maximum transmission torque is thus produced atpositions where a maximum stress is produced due to the deformation ofthe resilient members.

In the seventh means, power can be transmitted directly to an externaldevice through the power transmission means provided on the bearing ringat the driven side. Such a power transmission mechanism is compact andrequires a minimum number of parts. Thus, the torque limiter can becoupled to various machines at low cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing the torque limiter of a firstembodiment;

FIG. 2 is a sectional view taken along line II--II of FIG. 1;

FIG. 3 is a sectional view taken along line III--III of FIG. 1;

FIG. 4 is a view for explaining the creeping phenomenon in theembodiment;

FIG. 5 is an enlarged sectional view of the clutch portion of the same;

FIG. 6 is a sectional view of a second embodiment;

FIG. 7 is a sectional view taken along line VII--VII of FIG. 6;

FIG. 8 is a sectional view taken along line VIII--VIII of FIG. 6;

FIG. 9 is a sectional view of a third embodiment;

FIG. 10 is a sectional view of a fourth embodiment;

FIG. 11 is a graph showing the relation between the bending stress inthe leaf spring and the transmission torque;

FIG. 12 is a sectional view of a fifth embodiment;

FIG. 13 is a graph showing the relation between the bending stress inthe leaf spring and the transmission torque;

FIG. 14 is a sectional view of a sixth embodiment;

FIG. 15 is a sectional view taken along line XV--SV of FIG. 14;

FIG. 16 is a sectional view taken along line XVI--XVI of FIG. 14;

FIG. 17 is an enlarged sectional view of a portion of the same wherecreeping occurs;

FIG. 18 is a sectional view taken along line XVIII--XVIII of FIG. 14;

FIG. 19 is a sectional view showing the operation of the clutch of thesame;

FIG. 20 is a view showing a prior art torque limiter; and

FIG. 21 is a view showing another prior art torque limiter.

BEST MODES FOR EMBODYING THE INVENTION

FIGS. 1-5 show the torque limiter of the first embodiment. As shown inFIGS. 1 and 2, an inner ring 1 and an outer ring 2 are rotatablysupported by bearings 3 and 4 disposed at both ends thereof and held bythese bearings so as to be coaxial with each other.

The inner ring 1 has a cylindrical surface 5 on the outer peripheralsurface at its central portion. The outer ring 2 has on the innerperipheral surface a polygonal surface 6 which is a substantiallyregular octagon, so as to be opposite to the cylindrical surface 5. Arecess 7 having a predetermined length is formed in each side of thepolygonal surface 6 at the central portion thereof with respect to thedirection of length of the sides of the polygonal surface 6. A leafspring 8 in the form of a polygonal ring and having a shapecomplementary to the polygonal surface 6 is fitted in the outer ring 2.

The leaf spring 8 is fitted tightly or with a slight gap left betweenthe spring and the polygonal surface. Once fitted, it serves as atorsion beam having both ends thereof supported, with its corners inclose contact with the respective corners of the polygonal surface 6 andits central parts deformed toward and into the recesses 7.

The inner peripheral surface of the leaf spring 8 is formed by aplurality of engaging surfaces 9. A wedge space is defined between eachengaging surface 9 and the cylindrical surface 5 of the inner ring 1.The narrowest portion 10 of the wedge space has a width a which isslightly smaller than the diameter d of rollers 13 which will bedescribed later.

An annular cage 11 is also mounted between the engaging surfaces 9 ofthe leaf spring 8 and the cylindrical surface 5. The cage is provided inits circumferential surface with a plurality of pockets 12 arranged atequal intervals so as to be disposed opposite to the engaging surfaces9. The rollers 13 as engaging elements are received in the respectivepockets 12.

The rollers 13 have an outer diameter d which is smaller than the widthof the space between the engaging surface 9 and the cylindrical surface5 except at its narrowest portion 10. Thus, as shown in FIG. 1, therollers 13 engage the engaging surfaces 9 and the cylindrical surface 5only when they are located near the narrowest portions 10. Thus, thisstructure serves as clutch having a strut angle of θ.

The rollers 13 can pass the narrowest portion while deforming the leafspring 8 so as to expand the space between the leaf spring 8 and thecylindrical surface 5. When deformed, the leaf spring 8 serves as atorsion beam having both ends supported. By properly setting thethickness and deflectability of the leaf spring 8, the maximumtransmittable torque can be determined with high accuracy. If the loadexceeds this maximum torque, the rollers 13 are allowed to pass thenarrowest portion, so that the load is released.

As shown in FIG. 1, the inner ring 1 has, on the outer peripheralsurface, an eccentric surface 15 having an eccentricity of ε withrespect to the cylindrical surface 5. A bearing 16 is mounted on theeccentric surface 15. Thus, its outer peripheral surface is alsoeccentric from the axis of the inner ring 1 by ε.

The outer peripheral surface of the bearing 16 is in contact with theinner peripheral surface of the cage 11 through an O-ring 17. The cage11 is thus urged in a diametric direction so as to be held in aneccentric position with respect to the inner ring 1. In thisarrangement, the cage 11 is held in its eccentric position by aneccentricity imparting mechanism 14 comprising the eccentric surface 15and the bearing 16. Alternatively, the eccentricity imparting mechanismmay comprise a bearing 16 in the form of an eccentric bearing having aneccentric inner ring and mounted on a surface 15 which is coaxial withthe cylindrical surface 5.

The O-ring 17 made of a resilient material, serves to compensate for anydimensional error of the outer peripheral surface of the bearing 16 andthe inner peripheral surface of the cage 11, and to adjust the contactpressure between the bearing 16 and the cage 11. The bearing 3 providedbetween the outer ring 2 and the inner ring 1 supports the load produceddue to the fact that the bearing 16 is mounted in an eccentric position,thereby allowing the cage 11 and the outer ring 2 to creep smoothly withrespect to each other as described later.

On the other hand, the outer ring 2 is provided at one end thereof withan inwardly bent L-shaped portion 18. An annular portion 19 is providedon the outer peripheral surface of the bent portion 18 so as to bedisposed inside of an annular portion 20 provided on one end of the cage11. The outer peripheral surface of the annular portion 19 is acylindrical surface which is coaxial with the outer ring 2. As shown inFIGS. 3 and 4, its outer peripheral surface is partially in contact withthe diametrically offset inner peripheral surface of the annular portion20 of the cage 11.

The difference of engaging gap δ between the outer diameter DL of theannular portion 19 and the inner diameter DC of the annular portion 20of the cage 11 is set within the range of 1/300-1/2000 of the nominaldiameter D of DL and DC. (FIG. 1) In this arrangement, the offset amountof the cage 11, which is diametrically offset by the eccentric surface15 on the inner ring 1, is restricted by the outer diameter DL of theannular portion 19 and the inner diameter DC of the annular portion 20.Namely, the cage 11 is offset by a distance equal to 1/2 of the gap δ.Thus, the annular portion 20 of the cage 11 comes into contact with theannular portion 19 of the outer ring 2 at one point only.

In the figures, numerals 21, 22 and 23 indicate washers for preventingthe bearing 4 and the bearing 16 from coming into contact with otherparts. A sealing plate 24 is provided to seal lubricant.

Having described the structure of the torque limiter of the embodiment,we shall now describe its operation.

As shown in FIGS. 1 and 2, the inner ring 1 is coupled to a drivingmember and the outer ring 2 is coupled to a driven member. When theinner ring 1 is rotated in the direction of arrow with the rollers 13 inabutment contact with the cylindrical surface 5 of the inner ring 1 andthe engaging surfaces 9 of the leaf spring 8 in the form of a polygonalring, the rollers 13 will wedge into the space between the cylindricalsurface 5 and the engaging surfaces 9. A clutch having a strut angle θis thus established and the outer ring 2 and the inner ring 1 willrotate together.

As the torque applied to the outer ring 2 increases, the engagingsurfaces 9 of the leaf spring 8 forming the clutch deflect into therecesses 7 as shown in FIG. 5, so that the strut angle θ and thus thetorque applicable will decrease. If the outer ring 2 is continuouslysubjected to such an excessive torque, the rollers 13 will move past thenarrowest portions 10 to the opposite side of the engaging surfaces 8.Thus, the clutch is disengaged. The torque limiter of this embodimentserves as a safety device which prevents excessive loads by releasingany torque that exceeds a predetermined level.

Once the rollers 13 have gotten out of engagement, they will move at aspeed much slower than the inner 1 because the annular portion 20 of thecage 11 having pockets carrying the rollers 13 is kept in contact withthe annular portion 19 of the outer ring 2.

As the driving member is driven further and the inner ring 1 rotatesrelative to the outer ring 2, the cage 11 will rotate or creep, keepingcontact with the outer peripheral surface of the annular portion 19 ofthe outer ring 2 as shown in FIG. 4 by the action of the eccentricityimparting mechanism 14. Namely, as the annular portion 20 of the case 11rotates one full turn about the annular portion 19 of the outer ring 2,the former shifts relative to the latter In a circumferential directionby a distance equal to gap δ multiplied by π.

The cage 11 rotates in the same direction as the inner ring 1. But dueto the creeping of the cage, the number of revolutions Nc of the cage 11is expressed by Nc=(δ/φD)×N wherein N is the number of revolutions ofinner ring.

Because the gap δ is set within the above-described range, the cage 11rotates at a speed 1/300-1/2000 of the revolving speed of the innerring 1. If, for example, the number of revolutions per unit time of theinner ring 1 is 1800 rpm, the time T taken for the clutch to engageagain after it has been disengaged satisfies the following formula,provided the elastic polygonal ring 8 is octagonal in shape (havingeight corners):

    T=1/{(1800/60)×(1/300-1/2000)×8}=1.25-8.33 sec.

Thus, in the torque limiter of this embodiment, the clutch willdisengage if the torque produced exceeds a predetermined value. Thetorque is not transmitted in this state. But, several seconds later, theclutch re-engages automatically. Thus, even if the driven member shouldstop due to some abnormal state, enough time is allowed before theclutch re-engages. This torque limiter can be used especiallyadvantageously as a safety device for applications in which even if thedriven member should stop due to some malfunction, it usually recoversin a relatively short period of time. Such applications include a screwpropeller of a small craft and a compression circuit of a refrigeratorcompressor.

If the inner ring 1 rotates from the state shown in FIG. 2 in thedirection opposite to the direction shown by arrow, no torque istransmitted while the clutch is out of engagement. The clutch willre-engage automatically thereafter. Then the above-described operationis repeated.

The time taken after cutting off torque transmission until the clutchre-engages is adjustable by changing the gap δ between the outerdiameter of the annular portion 19 of the outer ring 2 and the innerdiameter of the annular portion 20 of the cage 11.

FIGS. 6 to 8 shows a second embodiment.

In this embodiment, the outer ring 2 has a front lid 31 and a rear lid32 which are press-fitted to the outer ring into the respective endsthereof. The outer ring 2 is rotatably supported by bearings 35 and 34disposed, respectively, between the front lid 31 and the inner ring 1and between the rear lid 32 and the inner ring 1.

The front lid 31 is provided on the inner surface thereof with a bentportion 31a which is bent toward the cage 11. The bent portion 31a hason the outer peripheral surface thereof an annular portion 19 which isinserted in an annular portion 20 provided on the front end of the cage11. A gap δ is provided between the annular portion 19 and the annularportion 20.

The annular portion 20 is provided in its inner peripheral surface withan annular groove 35 that completely encircles the surface. The innerring 1 is provided on its outer peripheral surface with an annulargroove 36 that encircles the surface at a position opposite to thegroove 35. Three rolling elements 37 in the form of steel balls arepress-fitted between the grooves 35 and 36. They are held by a ballretainer 38 so as to be arranged at circumferentially equal intervals(at the angular intervals of 120 degrees). As they roll in the grooves35 and 36, the cage 11 is guided in a circumferential direction withrespect to the inner ring 1.

The rolling elements 37 have a diameter Dw which is larger than the gapbetween the groove 35 formed in the cage 11 and the groove 36 formed inthe inner ring 1 so that the rolling elements 37 can be press-fittedbetween the cage 11 and the inner ring 1. By press-fitting the rollingelements 37, as shown in FIG. 8, the annular portion 20 of the cage 11is deformed with the apexes of deformation disposed at the contactportions with the rolling elements 37. Thus, it comes into contact atits deformed portions 39 with the annular portion 19 of the outer ring2.

Otherwise, this embodiment is the same in structure as the firstembodiment. Thus, like parts are denoted like numerals and theirdescription is omitted.

In the second embodiment, as the inner ring 1 and the outer ring 2rotate relative to each other, the rollers 13 are wedged into thenarrowest portions of the spaces defined between the cylindrical surfaceand the engaging surfaces 9. These rings thus come into engagement witheach other and rotate together. If an excessive load acts on the outerring 2 in this state, the leaf spring 8 covering the engaging surfaces 9is deformed, allowing the rollers 15 to pass the narrowest portions. Theclutch is now disengaged.

After having passed the narrowest portions, the rollers 13 are thenmoved toward the next narrowest portions by the cage 11. But since theannular portion 20 of the cage 11 is deformed due to the press-fit ofthe rolling elements 37 and kept in contact with the annular portion 19of the outer ring at a plurality of portions thereof, the cage 11 willcreep, thus causing the annular portions 19 and 20 to move relative toeach other by a distance equal to the engaging gap multiplied by thenumber π.

In this arrangement, the annular portion 20 of the cage 11 is broughtinto contact with the annular portion 19 of the outer ring 2 at threeportions. Thus, the contact load that acts on each of the annularportions 19 and 20 is dispersed, so that the surface wear of the annularportions 19 and 20 is less severe. This assures a prolonged life of thedevice.

FIG. 9 shows the third embodiment. In this embodiment, three pairs (sixin total) of rolling elements 37 are disposed between the cage 11 andthe inner ring 1, the respective pairs being arranged at angularintervals of about 120 degrees. Each of the rolling elements 37 is heldin such a position by the retainer 38 so that all the rolling elementswill revolve about the inner ring 1 at the same speed.

In the fourth embodiment shown in FIG. 10, two rolling elements 37 aremounted between the cage 11 and the inner ring so that the annularportions 19 and 20 will come into contact with each other at twoportions. In the alternative, two pairs (four in total) of rollingelements may be mounted, the respective pairs being disposed at anangular interval of 180 degrees.

The annular portions of the cage and the outer ring may be brought intocontact with each other not at two or three points but at four or morepoints by providing a necessary number of rolling elements.

In the above embodiments, as shown in FIG. 2, the side faces or theengaging surfaces 9 of the polygonal ring-shaped leaf spring 8 are flatso that the rollers 13 can slide smoothly thereon. Recesses 7 areprovided opposite to the central portions of the side faces of the leafspring 8 so that the leaf spring can be deformed at these portions.Since the leaf spring 8 is supported at both ends, its elastic strengthis low at its central portions and high at both ends. Thus, when therollers 13 are located near the narrowest portions of the spaces betweenthe engaging surfaces 9 and the cylindrical surface, the bending stressproduced in the leaf spring 8 is the greatest, as shown in FIG. 11, atthe central portions of the leaf spring 8 where the contact angle θ ofthe rollers 13 is zero. In contrast, the transmittable torque will bethe greatest at a certain contact angle and will be zero when therollers 13 are at the central portions where the elastic repulsion forceof the leaf spring 8 is the smallest.

Namely, whereas the actually transmittable torque is determined by therepulsion force produced by the deformation of the leaf spring 8 and thecontact angle of the rollers 13, if trials are made in the abovearrangement to increase the transmittable torque, the efficiency oftorque transmission is low because it is impossible to produce a maximumtransmission torque in a region where the leaf spring 8 is subjected toa maximum stress.

In contrast, the fifth embodiment shown in FIG. 12 is an embodiment inwhich the shape of the leaf spring is improved in order to solve theabove problem. In this embodiment, each engaging surface 9 of the leafspring 8 is provided at its central portion forming the narrowestportion of the space with a protrusion 41 protruding toward thecylindrical surface 5.

This protrusion 41 comprises two inclined portions 42, 43 provided atthe central portion of the leaf spring 8, where the contact angle θ iszero, so as to extend inwardly in symmetrical relation with each other.The angle β between each of the inclined portions 42, 43 and the tangentof the cylindrical surface 5 at a point where the contact angle θ iszero is determined at such a value that when the roller 13 engages theinclined portions 42, 43, it is held between the inclined portions 42,43 and the cylindrical surfaces 5, so that this device functions as aclutch (the angle should preferably be within the range of 5-15degrees).

In this arrangement, as the rollers 13 approach the narrowest portions,the leaf spring 8 is deformed toward the recess 7 provided behind it.When the rollers 13 get on the protrusions 41, the inclined portions 42,43 and the cylindrical surface 5 serve as a clutch with respect to therollers 13. By the wedging function of this clutch, the leaf spring 8will be markedly deformed outward, so that a large bending stress isproduced in the leaf spring 8. A large repulsion force is thus appliedfrom the leaf spring 8 to the rollers 13.

Thus, as shown in FIG. 13, the transmittable torque increases inproportion to the bending stress of the leaf spring 8 due to itsdeformation, which increases as the contact angle θ approaches zero.Since a maximum transmission torque is produced at a point where thebending stress of the leaf spring 8 reaches its maximum, a large torquecan be transmitted efficiently.

FIGS. 14 through 19 show a sixth embodiment.

In this embodiment, as shown in FIG. 14, the outer ring 2 has aplurality of belt grooves 51, 52 formed in its outer peripheral surface.The outer ring 2 itself thus serves as a power transmission pulley. Asshown in FIGS. 14 and 15, the inner ring 1, disposed at the drivingside, is formed with a bore 53 and a key groove 54 through which a driveshaft of an engine extends. The inner ring 1 is thus directly driven bythe engine.

Similar to the above embodiments, a cylindrical surface 5 is formed onthe outer peripheral surface of the inner ring 1 at its central portion.Spring seats 55 are formed on the inner peripheral surface 6 of theouter ring 2 opposite to the cylindrical surface 5 at 16 points arrangedcircumferentially spaced apart from each other. Eight spring leaves 8a,8b, . . . 8h are supported on the respective spring seats 55.

As shown in FIG. 15, with the spring leaves 8a-8h mounted on the outerring 2, they are arranged so that the pitches (or distances between theadjacent contact points with the rollers 13) are different from oneanother. The inner surface of each of the spring leaves 8a-8h serves asan engaging surface 9 which defines a wedge space in cooperation withthe cylindrical surface 5 of the inner ring 1.

The spring leaves 8a-8h are mounted on the respective spring seats 55 ina more or less tight-fit condition. A gap 7 is defined between each ofthe spring leaves 8a-8h and the inner surface of the outer ring 2 toallow for deformation of the spring leaves. Each of the spring leaves8a-8h is provided at its central portion with a protrusion 41 facing thecylindrical surface 5 of the inner ring 1. The spring leaves 8a-8h aredeformed when the rollers 13 get into contact with the engaging surfaces9 at portions near the protrusions 41.

An annular case 56 is mounted between the spring leaves and thecylindrical surface 5 of the inner ring 1. Eight pockets 57 are formedin the peripheral surface of the case 56 so as to be arranged at thesame pitches as the pitches between the spring leaves 8a-8h. A roller 13as an engaging element is received in each pocket 57. The outer diameterd of the rollers 13 is determined so that as shown in FIG. 19, they canpass through the space between each of the spring leaves 8a-8h and thecylindrical surface 5 by deforming the spring leaves 8a-8h toward thegaps 7.

As shown in FIGS. 17 and 18, the spring leaves 8a-8h are inserted untilthey abut a rear lid 58 press-fitted into the rear end of the outer ring2. The rear lid 58 has a flange 59 by which the spring leaves areresiliently deformed. The flange 59 is dimensioned so that its outerperipheral surface will abut the protrusions 41 provided on the innersurfaces of the spring leaves 8a-8h. This, each spring leaf, supportedat three points, i.e. at its protrusion 41 and the contact portions withthe spring seats 55, is held in a pre-tensioned, resiliently deformedstate. The spring leaves 8a-8h thus assembled will never drop out of theouter ring 2 nor will get out of position due to vibrations or the like.

On the other hand, the cake 56 has its front end protruding toward thebearing 33 and to this protruding end is coupled an annular membermounted coaxially with the inner and outer rings. An annular member 60has an annular portion 61 on its inner peripheral surface. The annularmember 60 and the cage 56 are tight-fitted together by engaging theprotrusions and recesses 67 provided at the inner periphery of theannular member 60 and at the end of the case 56, respectively. Thus, theannular member 60 and the cage 56 cannot move axially but are rotatablerelative to each other under a predetermined torque.

A front lid 62 having an L-shaped section is press-fitted into the frontend of the outer ring 2. On the inner surface of the front lid 62 isprovided an annular portion 63 fitted in the annular member 60. A spaceδ is defined between the annular portion 63 and the annular portion 61of the annular member 60.

As shown in FIGS. 16 and 17, a cylindrical roller bearing 64 is mountedbetween the annular member 60 and the cylindrical surface 5 of the innerring 1. It comprises an annular roller cage 65 and three cylindricalrollers 66 held by the roller cage 65 so as to be circumferentiallyspaced apart by 120 degrees from each other. As the rollers 66 roll,their rotation causes the cage 56 to rotate relative to the inner ring1.

The cylindrical rollers 66 have a diameter greater than the radialdimension of the gap defined between the annular member 60 and the innerring 1 so that they are press-fitted therebetween. Since the cylindricalrollers 66 are press-fitted, the annular member 60 is deformed by thecylindrical rollers in the same manner as shown in FIG. 8. The annularportions 61 and 63 come into contact with each other at these deformedportions.

In this embodiment, the drive shaft of an engine is fitted in thethrough bore 53 formed in the inner ring 1 and an external device at thedriven side are directly coupled to the belt grooves 51, 52 of the outerring 2 through power transmission belts. As shown in FIG. 15, as theinner ring 1 begins to rotate in the direction of the arrow, with therollers 13 kept in contact with the cylindrical surface 6 of the innerring 1 and the spring leaves 8a-8h, the rollers 13 will wedge into thespace between the cylindrical surface 5 and the engaging surfaces 9. Theclutch is now engaged and the outer ring 2 and inner ring 1 will rotatetogether. The driving force is thus transmitted from the outer ring 2directly to the external device.

As shown in FIG. 19 by dotted line, as the torque applied to the outerring 2 increases in this state, the spring leaves 8a-8h forming theclutch will deflect toward the recesses 7. If the outer ring issubjected to an excessive lead continuously for a prolonged period oftime, the rollers 13 will bass the narrowest portions. In this case, thelimiter torque T is set to the torque transmitted when all the springleaves 8a-8h deflect simultaneously.

When the engine keeps turning with no torque transmitted and the innerring 1 and the outer ring 2 rotate relative to each other, the annularmember 60 will creep while rotating about the outer periphery of theannular portion 63 due to contact between the annular portion 61 andannular portion 63. The rollers 13 thus move at a low speed to the nextengaging points.

During this movement, as shown in FIG. 19, assuming that the spring leaf8d first comes again into engagement with the corresponding roller 13,all the other leaf springs 8a-8c and 8e-8h are not in engagement withthe respective rollers because the pitches of the adjacent leaf springsare different from one another. Thus, the torque transmitted in thisstate is smaller than the limiter torque T. Thus, the initially settorque is not transmitted to the outer ring 2 at the driven side.

Similarly, the other spring leaves 8a-8c and 8e-8h come into engagementwith the respective rollers one after another. The torque transmitted ineach case is small because the eight spring leaves never come intoengagement with the rollers simultaneously.

Thus, all the rollers 13 engage and the predetermined torque istransmitted at time intervals eight times longer than the time intervalsat which all the rollers 13 engage when the leaf springs 8 are arrangedat equal pitches as shown in FIG. 2. This means that it takes eighttimes longer period for the torque limiter to reset to its originalposition.

As the rollers 13 move to the next engaging positions between thecylindrical surface 5 and the spring leaves 8a-8h and engage, the cage56 tends to rotate at about half the speed of the rotation of the innerring because it is adapted to rotate in the same manner as the rollerbearing. But since the annular member 60 is subjected to creeping, itshows a tendency to rotate at a much lower speed than the cage. Thus,there appears a difference in revolving speed therebetween. If thetorque produced by the difference in revolving speed exceeds thecircumferential locking force determined by the contact pressure betweenthe cage 56 and the annular member 60 at their tight-fit portions, thecage 56 and the annular member 60 begin to rotate relative to eachother, thus absorbing the difference in revolving speed. Thus, nosignificant slip will occur at the contact portion between the annularmember 60 and the annular portion 63 or between the rollers 13 and theinner ring 1. Their surfaces are thus less likely to get worn.

In the sixth embodiment, spring leaves are arranged at different pitchesfrom one another. But they may be arranged at equal pitches as in theother embodiments.

In the above embodiments, the inner ring was connected to a driving sideand the outer ring to the driven side. But this arrangement will operateexactly in the same way even if the inner ring is connected to thedriven side and the outer ring to the driving side.

Also, in the embodiments, the engaging surfaces 9 were formed by leafsprings so that the clutch can be released by deforming the leafsprings. But only portions of the engaging surfaces 9 or the cylindricalsurface 5 located near the narrowest portions may be made of a resilientmaterial such as rubber so that the rollers 13 can pass through thenarrowest portions by deforming the resilient material.

Industrial Application

As described above, according to this invention, between two bearingrings are formed a cylindrical surface and engaging surfaces which incooperation provide a plurality of engaging positions at which engagingelements come into engagement. The cage holding the engaging elementsrotate at a reduced speed with respect to the bearing ring at thedriving side. This makes it possible to rotate the engaging elements ata substantially lower speed, when they are moving from one engagingpoint toward the next. This means that it takes a longer time after thetorque transmission has been cut off by the clutch until the clutch isengaged again. Thus, the torque limiter according to the presentinvention permits an ample time for the machine to recover frommalfunction or for the operator to stop the machine if it has brokendown.

We claim:
 1. A torque limiter having an automatic reset functioncomprising two bearing rings fitted one on the other, one of saidbearing rings being connected to a driving side member and the other toa driven side member, said bearing rings having surfaces opposed to eachother, one of said opposed surfaces being a cylindrical surface, theother of said opposed surfaces being engaging surfaces, a cage formedwith a plurality of pockets and mounted between said bearing rings,elastically deformable engaging elements each received in said pocketsand adapted to engage said cylindrical surface and said engagingsurfaces, said engaging surfaces having their portions to be broughtinto contact with said engaging elements, and a decelerating meanscomprising an annular portion provided on said bearing ring connected tosaid driving side member and an annular portion formed on said cage,said two annular portions being kept in rolling contact with each otherso that the cage is rotated at a lower speed than the bearing ringconnected to the driven side member while said engaging elements are notin engagement with said bearing ring connected to said driving sidemember.
 2. A torque limiter as claimed in claim 1 wherein said engagingsurfaces form a polygonal surface.
 3. A torque limiter as claimed inclaim 1 or 2 wherein said two annular portions are concentrically fittedone on the other with a gap defined therebetween and adapted to rotatetogether with said bearing ring connected to the driven side member andsaid cage, respectively, and said decelerating means further comprisesan eccentricity imparting means for offsetting one of said annularportions to bring it into contact with the other annular portion.
 4. Atorque limiter as claimed in claim 1 or 2 wherein said two annularportions are fitted one on the other with a gap defined therebetween andadapted to rotate together with said bearing ring connected to thedriven side member and said cage, respectively, and said deceleratingmeans further comprises rolling elements press-fitted between said cageand said bearing ring connected to the driving side member for bringingsaid annular portions into contact with each other by deforming theannular portion adapted to rotate together with said cage.
 5. A torquelimiter as claimed in claim 1 or 2 wherein said engaging surfaces havetheir engaging portions formed of plate-shaped resilient members, andwherein recesses are formed in said bearing ring adjacent said resilientmembers on a side thereof opposite said cylindrical surface to permitdeformation of said resilient members.
 6. A torque limiter as claimed inclaim 5 wherein said each resilient member is provided with a protrusionextending toward said cylindrical surface.
 7. A torque limiter asclaimed in claim 1 wherein the bearing ring connected to the driven sidemember is integrally provided with a means for transmitting power.